An increasing number of people are experiencing problems with their back. One reason for this is assumed to be the way people are living spending a large part of the day sitting in conventional chairs, in cars or public transport means, in the office, and at home in the evening sitting in a recliner watching TV. This passive lifestyle leads to the muscles supporting the spinal column being under-stimulated and therefore reducing in size. Even in persons training regularly, these so-called core muscles are often under-stimulated. The core muscles are intended to support the body through a whole day of physical activity. Then, the core muscles will work automatically in stabilizing the back when the body is in motion. However, training a couple of evenings a week is not enough to support the core muscles. Due to modern lifestyle these muscles are often so weak that the automatic stabilizing action no longer works as it should. The result is pain due to sliding discs and strained muscles.
Another effect of under-stimulated core muscles is that the ability of keeping balance is impaired. This is particularly evident in elderly people who become dependent on roller chairs or other accessories, and often fall and become injured. The loss of balance is a problem for many elderly people. Even though this partially may be a consequence of age, there is an increasing belief that this effect mainly is caused by lifestyle, i.e. lack of physical exercise and time spent in improper chairs.
The present inventor has identified the common chair as one cause of these problems, and has since the 1970's tried to develop a better chair suited to modern lifestyle. The first result of this work was the so-called “Balans@ chair”. One version of this chair is described in Norwegian patent 145973. This chair includes a flat seat that is tilted forward and a leg support mounted in front of the seat. A person sitting on such a chair will straighten the back and obtain a position where the body is balanced along an axis through the body's centre of mass. This position is akin to a person on horseback, or the position often seen practiced by children sitting on the floor with the legs folded beneath them. This balance occurs naturally when standing, walking or running, and this chair allows a user to obtain such a balance also when sitting. However, this chair had a number of shortcomings, among others that the users complained of too large pressure on the knees. Thus, the inventor developed an improved version disclosed in Norwegian patent 320859. This chair includes a saddle seat and a leg support, the distance between the seat and the leg support being adjustable. The design of the saddle seat was later improved in Norwegian patent 328285.
There has been a trend in later years to provide working places with tables which are electrically adjustable in height. Thus, the worker may lift the table top and work in a standing position. When this standing position gets wearing, the users may lower the table and continue working sitting on a chair. However, one reason for the standing position soon becoming wearisome is that the back is not properly supported by the core muscles, as mentioned above. Also, a flat, hard floor may be hard for the feet, as people are designed to move in an uneven terrain, not on a flat floor.